I found out what the problem was. Instead of downloading the file to the base TitanNetworks\Mids directory, it was dumping the MHD.MHZ file in the ...\Images\Sets subdirectory. Once I found the damned file and moved it to the correct location, it finally updated.
This is very frustrating, when you don't have control over where a file gets put, no knowledge of where it gets put, and it just automatically is dumped wherever the program was last pointed to.
Either be precise on where a file must be downloaded to, or allow the user to specify.